Continuous production of citric acid with recirculation of the fermentation broth after product recovery

An airlift reactor with double net draft tubes was developed. A sparger was located between the two draft tubes. The draft tubes had a significant effect on breaking bubbles into smaller ones. The assessment of the reactor performance was based on gas holdup, mixing time, and volumetric mass transfer coefficient. The proposed reactor had higher gas holdup and volumetric mass transfer coefficient, and lower mixing time in comparison with those of the bubble column. Application of the proposed reactor to fermentation of Saccharomyces cerevisiae demonstrated that the cultivation time was significantly shortened.